i'm getting ready to build my frist motor. it's going in a 85 Blazer. i found a 350 4bolt main and i was wonder if there's a difference in the newer 350 and the older ones. in about 85 or so they went to the 1 peice rear main seal just means the cranks are different. i guess what my question is what a good year or years to go with and what years are to stay away from. i'm looking to get about 400hp out of it and i want it to be a low end motor. thanks

I am sure the Chevy guys can come up with lots of little nitpicky things to show how one is different....but really....they are Chevy 350s and everything is interchangeable and they all pretty much rule. But don't tell the Dodge guys I said that or I will claim and moderate you till the end of the earth comes.

Happy "one-of-these-damn-electrical-thingys-no-workie-must-find-which-one" Hunting!!!
On the Peenneensoola!
I have a degree in Emergency Drivetrain Repair on the Side of the Road with level IV certification.

from what i know from talkin to my uncle the other day he was saying if i was to put a 350 in my truck to try and find a 4 bolt main no matter what year it is cause the 4 bolts were the best but there hard to find cause the stock car boys all blew them up he was sayin that the 4 bolts could stand alot higher rpms then 2 bolt mains and would last longer under stress

You can run a 4 bolt block if you want, but make sure it has 010 stamped on it. If not then keep searching. Personally I would find a 2bolt main block and put splayed caps on it and have the machine shop drill and tap the hole. Then you have a very strong 4 bolt block. The stock 4 bolt blocks not stamped 010 were a weaker block with less nickel content, hence why there are 4 bolts. The one piece seal block however in the HD version with 4 bolt caps are very strong. I would still run splayed caps though, if you plan on DD it dont run billet caps, they will expand at a different rate then the block and cause abnormal bearing wear. The rods and bore and deck height is the same either block, also the heads are the same mounting. The intake got changed in 87 though, the two center intake bolts are at a slightly different angle, but a die grinder will fix any intake to work an a hour or so. Also when you look at a chevy SB in the front of the block there are 3 oil galley plugs that get pressed in. (behind the timing cover) I recommed to people to have then tapped for a plug (same one used on the back of the block) and then on the top center one drill a very small hole in it. This will cause very good lubrication to the timing chain. In 1976-77 they changed the front oil pan seal to a thicker seal, so you need the correct oil pan set gasket to work. Also in 1979 the dipstick changed sides, need an oil pan accordingly. Other then that, the only thing I think is different but dont know for sure, is I think the crank centerline is different in a one piece seal block, then a two piece seal block. I think there is more milled from the starter pad on the newer blocks, because the new starter wont align itself on older blocks.

Hope I didnt write to much for you, any questions on SBCs and shoot away. I studied this engine for a long time before I built my 383.

i'm curious how your gonna get 400h.p. out of a 350 ,with any low end. your gonna have to run a fairly large cam that wont live till higher rpm, and/or pay for super unleaded premium because of high compression ,i may be wrong. I think i'd rebuild a 400 small block with splayed caps , ported and polished double hump heads and 9.1:1 compression ,but then again thats just my opinion.

Splayed caps are stronger than caps that run all the mains in parallel. All the production 4-bolt main blocks run parallel fasteners/bolts. If you think you NEED 4-bolt main caps, find a 2-bolt block and invest in a set of aftermarket splayed bearing caps & hardware. Milodon, for example, manufactures them for quite a few applications. With hopes of making 350-450 horsepower, I don't think you need 4-bolt mains, especially if you're not going to turn a whole bunch of rpm. Just invest in a good set of main bearing studs...not bolts.

FWIW, the strongest production smallblock Chevrolet block ever cast by GM was the 509 (last 3 digits of the casting number are 509) 2-bolt main smallblock 400 block. They have very thick bulkheads and webbing in the block. They are, when retofitted with splayed 4-bolt caps (like referenced above) and good hardware, nearly as strong as a GM Performance Parts "bowtie" block.

I'd just slap on a Edelbrock intake, carb, cam, and some headers and I'm sure you'll be around 400hp. Check the Edelbrock site, they have a bunch of dyno proven combos you can buy. You won't need anything that crazy to get a 400hp small block.

dont set yourself short,buy a set of vortec heads,the ones machined for more lift,run a good size 4x4 cam with decent lift and duration,roller rockers,headers,good dual plane intake,carb,and voila....450 hp on pump gas

obviously its a bit more detailed then that...but theres no way you can beat vortecs for the money,dont waste time porting old technology heads,or rebuilding them.